There are various types of bicycle hydraulic systems. For example, a bicycle hydraulic brake system includes a hydraulic operating device, such as a brake lever device, and a hydraulic operated device, such as a brake caliper. In the hydraulic operating device, a master piston is moved in a master cylinder in accordance with the pivoting of an operating portion such as a brake lever. When the master piston moves, fluid (oil, for example) is discharged out of the master cylinder and moved through a hydraulic hose to drive a slave piston in a slave cylinder of the hydraulic operated device.